C# Schema Definition

C# applications define the database classes to be managed in the eXtremeDB runtime using native C# class syntax applying special attributes.

For example, the following code snippet would define a database with two classes Department and Employee:

 
    [Persistent]
    class Department
    {
        [Indexable(Type = Database.IndexType.BTree, Unique = true)]
        public String code;
        public String name;
        [Indexable(Type = Database.IndexType.Hashtable, Unique = true)]
        public int dept_no;
    }
     
    [Index("byDept_EmployeeName", Keys = new string[] { "dept_no", "name" }, Unique = false)]
     
    [Persistent]
    class Employee
    {
        [Indexable(Type = Database.IndexType.BTree, Unique = true)]
        public String  name;
        public int  dept_no;
    }
     

Note that the attributes [Persistent], [Indexable()]and [Index()] are used to specify the classes and indexes to be generated and maintained in the database.

eXtremeDB C# Database Attributes

The attributes that are recognized as eXtremeDB database specifications are as follows:

Persistent

Class attribute: Marks this class as “stored in the database” and optionally provides some attributes of this class;

• Persistent(autoid=true) - Creates an autoid index
• Persistent(list=true) - Creates a list index
• Persistent(large=true) - Declares the standard storage model (default)
• Persistent(compact=true) - Declares the compact storage model
• Persistent(inmemory=true) - Declares this class as in-memory (default)
• Persistent(disk=true) - Declares this class as disk-based (i.e on persistent storage media)
• Persistent(local=true) - Declares this class as local for eXtremeDB High Availability partial replication

Index

Class attribute: Defines a compound (multi-field) index; possible properties are:

name="indexName"

Identifies this index

keys={Key(“field1”) [, Key(“field2”) …] }

List of key fields

unique=true

Creates a b-tree index (the default), true enforces uniqueness; if false allows duplicates

thick=true

Optimized for a large number of duplicates

descending=true

Indexes are ascending by default

initSize=N

For hash indexes; N is the initial size of the hash table

type=Database.IndexType.BTree

Possible Database.IndexType values are:

• BTree - Creates a tree index (the default)
• Hashtable - Creates a hash index
• Patricia - Creates a patricia index
• RTree - Creates an rtree index
• RTreeOfPoint - Creates an rtree index
• KDTree - Creates a kdtree index
• Trigram - Creates a trigram index

for example:

 
    [Index(name="byName", keys={ Key("lastName"), Key("firstName") }, unique=true )]
     
    class Employee
    {
        String  firstName;
        String  lastName;
        Address address;
        long    salary;
    }
     

Indexable

Field attribute: Specifies an index on the following field. The index will have the same name as the field. With the exception of name and keys properties, the possible properties are the same as for class attribute Index (above).

for example

 
    class Obj
    {
        [Indexable(Type=Database.IndexType.BTree, Unique=true)]
        public int value;
    }
     

Encoding

Field attribute: Specifies the encoding of string fields. Can be any valid encoding supported by the C# runtime. UTF-8 is the default. Examples:

     
    [Encoding("UTF-16")]
    String s1;
    [Encoding("ASCII")]
    String s2;
     

Blob

Field attribute: Uses eXtremeDB BLOB type for storing a byte array; for example:

 
    [Blob] public byte[] photo;
 

Dimension

Field attribute: Specifies the dimension for fixed size arrays (char, scalar) An array without a dimension will be treated as a vector (dynamic array). Example:

     
    [Dimension(8)]

    String prefix;


     

Numeric

Field attribute: Specifies the width and precision for decimal fields. Example:

     
    [Numeric(12,3)]

    decimal d;
// Equivalent to decimal<12,3> d;

     

Binary

Field attribute: Specifies a fixed length Binary field. Example:

     
    [Binary(100)]

    byte[] dim100_binary;
// A Binary array of 100 bytes

     

Varbinary

Field attribute: Specifies a variable length Binary field. Example:

     
    [Varbinary]

    byte[] var_binary;
// A Binary vector (dynamic array)
     

Nullable

Field attribute: Specifies that this field can be null. The C# "?" syntax will also produce a nullable database field. Example:

     
    [Nullable]

    bool isALive; // Explicitly declared nullable field
    bool? isDead; // Imnplicitly declared nullable field
     

Optional

Field attribute: Defines a structure field as optional; for example:

     
    [Optional]
    NestedStruct opt_nested;
     

References

Field attribute: Used to declare a field of type ref which refers to a Class in the schema; for example:

     
    [References(ClassA)]
    ulong a;
     

SQL column names and C# fields

When using SQL tables associated with C# classes, be aware that the SQL column names are case sensitive. The SQL table column names will correspond to the exact upper and lower case names used in the C# persistent classes.